Four more Democratic senators will co-sponsor Sen. Bernie Sanders' Medicare-for-all bill, Mic reported Monday. Sen. Cory Booker of New Jersey and Sen. Jeff Merkley of Oregon publicly announced that they would co-sponsor the bill, which Booker had previously been slow to endorse. Sources close to Sen. Kirstin Gillibrand of New York told Mic that Gillibrand intends to co-sponsor the legislation. Sen. Brian Schatz of Hawaii confirmed that Schatz also plans to sign on as a co-sponsor. The senators join colleagues Elizabeth Warren, Kamala Harris, and Ed Markey in sponsoring the legislation, which is slated for introduction Wednesday. Political analysts have viewed support for the bill as a signal of potential interest in running for president in 2020.